They say history is written by the winners of wars.

History is written by the writers with the most popular narrative. Military hegemony is the most common way to ensure your narrative's popularity, but it's not the only way.

I think that there are just as many counter examples of this as there are confirmations. The Mongols are probably the best counter example.

Counter-examples: The Vikings. Most of the history of the Viking was by Christian monks in England and the like, who were the victims of the Vikings.